Yamaha F90 Shift Shaft Binding/Sticking

Did a water pump service on my lower unit. Put the lower back on, and it wouldn't go into reverse unless you rotate the prop slightly. Took it off, indexed the male section on the lower unit to neutral. Re-installed the lower again. Now it won't go into forward unless you rotate the prop slightly. I've taken the lower unit off and reinstalled over 50 times. I've put it on in forward, neutral, and reverse. I get the same result. It's like I'm a "tooth" off in the shift shaft coupling. Only forward or only reverse will work. It's one or the other, unless you manually turn the prop shaft. When I do this, it kind of "snaps" back in. It isn't the control cables or binnacle. When I reinstall the lower, the shift shaft slides in fine- EVERY time. But it still won't work. I am at a loss. Any help would be appreciated!!!!

When you say "it won't go into reverse unless you rotate the prop slightly", does that mean you're not running the engine?

Have you tried moving control lever to forward or reverse, then install LU with gear in respective position? There is a chance with control lever in neutral and LU in neutral when reinstalling, the mid section shift shaft will knock the LU shift shaft out of neutral. Installing LU when in it and control arm are in gear prevents this.